The effects of deafferentation of the vomeronasal, olfactory or both systems of male mice on ultrasonic vocalizations in response to a male or female stimulus were analyzed. Regardless of the technique used, disruption of the vomeronasal system led to consistent reductions in ultrasonic vocalizations. Each animal receiving vomeronasal tract cuts, bulbectomies or a combined treatment of vomeronasal tract transection and intranasal flush with ZnSO4 markedly suppressed responding to the stimulus animals. Animals treated with intranasal ZnSO4 alone or those receiving control procedures continued to respond to the female stimulus animals at rates similar to pretreatment. These results indicate that the vomeronasal system is directly involved in the perception of female mouse chemosignals and, hence, mediates the male's responses to these signals.